Tech Briefs

Juvenile fish collection system modified at Cowlitz Falls

Preliminary results from operation of a modified removable fish collection system at the 70-MW Cowlitz Falls project indicate that fish rejection at a key location has been reduced to about 25 percent. However, the net entrance trap, added in 2007 to keep fish inside the structure, could be causing delay and rejection. Lewis County Public Utility District (PUD) is studying alternatives for this trap.

The original prototype was put in place for the 2006 migration season. Results from that installation were used to make decisions regarding improvements in fish passage for 2007.

Lewis County PUD installed the modified collection system for the 2007 migration season. The PUD says the purpose of the system is to aid in collecting downstream-migrating juvenile coho, steelhead, and spring chinook. Once collected, the fish are transported below the downstream 162-MW Mayfield Dam, owned by Tacoma Power.

Cowlitz Falls Dam is a hydrocombine design, with spillway bays for flood passage located directly above the turbine intakes. The fish collection system is installed in the spillway bay leading to Unit 2.

The system consists of baffle panels located at the entrance to the spillway bay, a screen that smoothly accelerates fish to a transport flume, and fish sorting and loading facilities.

The aluminum screen consists of six columns of rectangular screen panels in the walls, to allow dewatering of the system. The screen panels are formed using stainless steel profile bars to provide openings 1.75 millimeters wide. The final section of the screen has solid walls to provide smooth flow acceleration. The sections narrow as they reach the entrance to the transport flume, and the floor of the screen, which is solid, slopes up gradually to the entrance to the flume.

To attract fish to the system, a collection flow of 140 to 340 cubic feet per second is drafted through an opening in the baffle panels and down the turbine intake gate slots in the floor of the spillway bay. Once they enter the collection system, fish are transported directly to the fish flume. This prevents fish from being entrained by the attraction flow down the intake gate well slots, while still allowing the majority of fish collection flow to be used for power generation.

The design attempts to both collect the fish already entering the spillway bay and increase the percentage of fish entering this area.

The collection system can be removed via the gantry crane at the project to pass flood flows or for cleaning.

Modifications made as a result of the 2006 installation include: adjusting a fish flume gate to reduce flow; making the baffles that control the porosity of the screen adjustable to allow changes based on turbine flow levels; and adding the net entrance trap to guide fish into the opening at lower velocities, while making it hard to find the opening to get back out

The fish collection system at 70-MW Cowlitz Falls features walls made of rectangular screen panels, with a solid floor that slopes up gradually (at left). From the entrance to the collection system, the walls narrow (at right) to accelerate fish into the flume.

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Lewis County PUD is using the 2007 results to further improve the system.

MWH Americas Inc. and ENSR developed the hydraulic and structural designs for the new fish collection system. Farwest Iron Works Inc. built the system.

DOI releases guide on adaptive management

The U.S. Department of the Interior (DOI) announces availability of a new guide on adaptive management. The guide outlines the circumstances under which adaptive management is applicable and highlights the opportunities and limitations of this process. The 86-page guide is called Adaptive Management: The U.S. Department of the Interior’s Technical Guide.

DOI agencies – including the Bureau of Reclamation – are regularly faced with complex land and water management decisions, often with uncertain or incomplete information, says Tara Conrad, special assistant in the office of the DOI assistant secretary of water and science. Adaptive management is a tool for these agencies to use to improve resource management decisions under conditions of uncertainty, when flexibility exists, while accruing more information, Conrad says.

The guide:

– Defines adaptive management;

– Identifies the conditions under which practitioners should consider adaptive management;

– Outlines the process for implementing adaptive management; and

– Suggests a process for evaluating the effectiveness of adaptive management.

Hydropower Generation Report

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In addition, the guide includes case studies of successful applications of adaptive management. One such case study for the hydro industry is the Glen Canyon Dam Adaptive Management Program. This plan was developed to provide a process for cooperative integration of dam operations, downstream resource protection and management, and monitoring and research information, Conrad says. For details on the use of adaptive management at Glen Canyon, see the article “Glen Canyon Dam Experimental Flows: Employing Adaptive Management Concepts,” Hydro Review, Volume 22, No. 6.

– To access the guide, visit the Internet: www.doi.gov/initiatives.html and click on Adaptive Management.

USSD releases white paper on materials for embankment dams

The U.S. Society on Dams (USSD) announces publication of a white paper, Strength of Materials for Embankment Dams. The paper summarizes experiences with regard to selecting fill strength parameters and performing static analysis of earthfill embankment dams.

The purpose of the paper is to present the state-of-practice in these areas. To do this, USSD surveyed dam owners, regulators, and engineering consultants. The paper summarizes the approach each respondent provided regarding static stability analysis, loading conditions, shear strength parameters, field and laboratory testing, procedures for interpreting test results, factors of safety, and methodologies used for static analysis.

Chapters in the white paper cover:

– Loading conditions for embankment dams;

– Determination of shear strengths; and

– Static analysis of embankment stability.

USSD’s Committee on Materials for Embankment Dams prepared the white paper, which supercedes the previous version published in June 2006.

– To print a copy of the white paper, visit the Internet: www.ussdams.org/ reports.html.